Now you can edit configuration in /etc/named.conf and mappings in /var/named. Then both named and named-chroot can be used (one at a time of course). Restarting named-chroot recreates the chroot applying configuration changes. You should never edit config files residing in the chroot. This should be considered essentially as read-only.

$TTL defines the default time-to-live for all record types. 7200 are seconds so its 2 hours.

Serial must be incremented manually before restarting named every time you change a resource record for the zone. If you forget to do it slaves won't retransfer the zone: they only do it if the serial is greater than that of the last time they transferred the zone.